As counterfeiters become increasingly sophisticated in creating counterfeit secure documents (either from scratch or modifying valid documents), there is need for increasingly effective security measures to thwart them. One way to thwart counterfeiters is to insert features into documents that are difficult to reproduce. In some cases, these features are intended to be covert so that it is difficult for the counterfeiter to even identify their presence on the document. As an additional layer of security, these features should have a linking relationship with other features that interlock the features to increase the difficulty in accurately reproducing the relationship and show evidence of tampering when the relationship is broken. Finally, these features should include a means to provide forensic tracing capability so that analysis may be applied to trace the document to its source (e.g., manufacturer, printer, lot, operator, etc.). This enables detection and perhaps identification of an invalid source (or confirmation of a valid one) as well as useful information about the source for law enforcement.
The attributes identified above are needed for a broad spectrum of secure documents, and are particularly useful in identification documents. To provide context for forensic security features in identification documents, a description of these documents and methods for creating them follows below.